<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div ,p{
            width: 250px;
            height: 30px;
            color: #fff;
            background-color: pink;
        }
    </style>
</head>
<body>
    <button>显示当前系统时间</button>
    <div>某个时间</div>
    <p>123</p>
    <script>
        var btn = document.querySelector('button');
        var div = document.querySelector('div');
        btn.onclick = function() {
            div.innerText = getDate();
        }
        function getDate() {
            var date = new Date();
        var year = date.getFullYear();
        var month = date.getMonth() + 1;
        var dates = date.getDate();
        var arr = ['星期日','星期一','星期二','星期三','星期四','星期五','星期六']
        var day = date.getDay();
        return '今天是:' + year + '年' + month + '月' + dates +'日' + arr[day];
        }
        //
        var p = document.querySelector('p');
        p.innerText = getDate();
    </script>
</body>
</html>